Automatic telephone system



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. arrangement for ringing when a reverting call is ma ists of lesserimportance in Patented I. May 19, 1931 UNITED STATES PATENT OFFICECOMIPANY, OF CHICAGO,

NORMAN H. SAUNDERS, OF HOMEWOOD, ILLINOIS, ASSIGNOR TO RESERVE HOLDINGILLINOIS, A COBZPORATION DELAWARE AUTOMATIC TELEPHONE SYSTEM Applicationfiled May 8, 1929. Serial No. 361,311.

- The present invention relates to automatic telephone systems ingeneral, but is concerned more particularl with the development of asmall unattende exchange designed to serve a small town and thesurrounding community; and the broad, general object is the productionof new and improved circuit arrangements whereby the apparatus issimplified and improved.

A further object is the provision of suitable circuit arrangements fornotifying an attendant at a nearby attended exchange when an abnormalcondition arises within the unattended exchange of sufiicient gravity towarrant the dispatching of a repairman to the unattended exchange tomake an ads justment or to perform a repairing operation. It is afurther object to provide suitable arrangements for giving the attendantat the attended exchange a distinctly different signal in case anabnormal condition exthe unattended exchange. Itis a feature of thearrangement that both indications may be given over a trunk line betweenthe attended and unattended exchanges while ceeding over the trunk linewithout interfering with the conversation.

A further object is to provide an arrangement such that a connectoraccessible to the lineswitch of a calling line is not used in case it isout of order.v This object is realized plunger line automatically by theuse of switches of the so-called self-aligning type. When the individualfuse of a connector is blown the line relay fails to respond and thebecause the trunk tests Since the plunger is self-aligning a In case thedefe at in the connector consists 1n its sticking in an oilnormalposition, special arrangements are provided for causing the trunkleading to the connector to test open so as to cause the lineswitch torelease and automatically realign on a new trunk.

A further object is to bagk on party lines A further object is toprovide a simplecombination one-digit and two-digit connector aconversation is pro-.

' its operation will provide a simplified which is operated inaccordance with two digits when a subscribers line is being called andis operated in accordance with only one digit in making certain othercalls to be hereinafter explained.

It is a further object to make provisions for preventing the tying up ofall calls to a trunk group by an open or other defective condition ofthe first trunk of the group In addition to the foregoing, there areother objects and features of the invention which will be understoodbest upon a further perusal of the specification in connection with 4General description Figs. 1 to l show certain -switching apparatus m anattended manual exchange an in an unattended communit automatic exchange(abbreviated C. A. changes are interconnected by the trunk'line TLlextending between Figs. 1 and 2; Figs. 5 to 8 show certain apparatusknown as power and supervisory apparatus auxiliary to the switchingapparatus in the C. A. X.; and Figs. 9 and 10 show a desirablemodification of the apparatus of Figs. 3 and 4, respectively; Fig. 11shows the code sent out by the code interrupter apparatus of Fig. 7;Fig. 12 shows the sheets on which Figs. 1 to 8 are drawn should beplaced; and Fig. 13 is a layout of Figs. 9 and 10.

Detailed clescajption A general description of the apparatus having beengiven, a detailed description of now be proceeded with. For this purposeit will be assumed that the subscriber at substation'Al desires toconverse with the subscriber at substation A2.

Local call in the 0. A. X.

When the receiver is removed at substation A1, line relay 304 oflineswitch LS1 operates over conductors 301 and 303 and places The twoex-v the accompanying drawings comprising Figs. 1

2 Qrsomae ground on the private normal conductor 302 at itsupperarmature, at the same time closing a circuit for the pull-down windingof the magnet 305 at its lower armature; By

5 the ground potential on conductor 302, the

line of substation A1 is made. busy immediate] to the connectors,and,-by the closure 7 of t e circuit through the lower winding of magnet305, the plunger arm 306 is operated to force the bank contact springsinto engagement. This extends the conductors 301303 into engagement withconductors 308310, respectively. As a further result of the operation ofthe plunger arm 306, thelocal contact springs thereof connect the upperwinding (the bridge-cutoff winding) of magnet 305 to the groundedconductor 302 r to form a holding circuit for the lineswitch.

Upon the operation ofthebridge-cut-ofi' arm 307, which occurs responsiveto the energization of magnet 305 by either winding,

line relay 304 and ground are disconnected from conductors 301 and 303,respectively. Relay 304, being slow acting, does not fall backimmediately. p

Responsive to the extension of the grounded conductor 302 to conductor309, start relay 311 of'the master switch MSl operatesthrough test wiper312 and over a branch of conductor 309 and preselects an idle trunk inthe usual manner. a

In the local connector L01, line relay 323,

whose lower winding is connected to conductor 310 by way of contacts ofrelays 322 and 321 and whose upper winding is connected to conductor 308by way of oil-normal contacts 332 and contacts of relays 322 and 321,

operates over the calling line and closes a circuit for release relay324 in series with 40 the vertical magnet 335. The vertical magnet doesnot operate ate/this time owing to the relatively high resistance ofrelease relay 324. Release relay 324 operates and places ground on therelease trunk conductor 309 at 1ts upper armature, closing a holdingcircuit for the lineswitch LS1 through the upper winding of magnet 305by way of the local contact springs of plunger arm 306. This circuit isclosed before the slow-acting relay 304 has had time to fall back.

.As a further result of the operation of relay 324, oil-normal contacts332 are shunted at the inner-upper contacts of the relay and ground isplaced on locking conductor 344 65 at the middle-upper contacts. Thisprepares a locking circuit for relays 326, 330, and 331 and closes acircuit through oil-normal contacts 334 for the upper winding of relay326. Relay 326 operates and prepares an operating circuit for verticalmagnet 335 at its inner-lower armature. r

At the lower armature of relay 324, a point in the circuit of releasemagnet 336 is opened and ground potential is extended to the tonestartconductor 621 which extends to Fig. 6,

operating the tone-start relay 809 by way of conductor 623, with resultsto be pointed out hereinafter. Thisground potential is supplied throughthe low-resistance shelf relay 376, common to a shelf of connectors.Relay 376 does not operate because of the relatively high resistance ofthe tone-start relay 809. The connection having been extended from theline of substation Alto the. connector LCl, and relay 326 having beenoperated, dial-tone current now passesirom conductor 811 to the lowertalking conductor through contacts of relays 330 and 326 and from thenceto the calling substation, informing the calling subscriber that he maynow dial he desired number.

lVhe'rFthe calling device (not shown) at substation A1 is manipulated inaccordance with the first digit 8 in the desired number, the linecircuit is interrupted a corresponding number of times and line relay323 of the connector LCl falls back momentarily each time the linecircuit is interrupted. Each time it falls back, line relay 323 opensthe initial circuit of relay 324 and short circuits relay 324 bygrounding its lower terminal. Eac time relay 324 is short circuited, adirect circuit is closed for the Vertical magnet 335 by way of theinner-lower contacts of relays 321, 324, 327 and 325, and the innerlower armature, operated, of relay 326.

Each time the short circuit is removed from relay 324 upon thereoperation of relay 323, the vertical magnet 335 restores.

By the operation of vertical magnet 335, the wipers 339-343 are raisedstep by step to the desired level of bank contacts. Althoughshortcircuited. momentarily each time the line relay falls back, relay324 remains operated due to the circulating current through its winding.Relay 329 operates in multiple with the verticalmagnet 335 each timerelay 324 is short circuite-d and it remains operated throughout theseries of impulses in series with relay 324, but it is unable to remainoperated indefinitely in series with relay 324 owing to the relativelyhigh resistance of the latter and owing to the shunting effect of magent335. Therefore, relay 329 falls back shortly after the, termination ofthe vertical movement. While operated, relay 329 maintains a lockingcircuit for relay 326 at its inner-upper armature through the upperarmature of remagnet 338, the wipers 339-342 are rotated Upon 'er thecalled line is busy or idle.

into engagement with the set of bank contacts in the eighth level inwhich the line of substation A2 terminates. This bank contact set isshown in the drawings as the first contact set in the eighth level.Accordingly, thc second digit dialled is the digit 1. The vertical wiper343 is rotated out of engagement with its contact bank, with which itmakes sliding engagement during the vertical movement.

Relay 329 is again operated during the rotary movement, this time inparallel with the rotary magnet. 'At its upper armature it closes acircuit for the auxiliary relay 328. Upon operating relay, 328disconnects test Wiper 340 from the test windings of relays 321 and 330and connects it instead to the winding of busy relay 327, while relay329, at its middle lower armature, places a shunt around the inner lowercontacts of busy relay 327 so as to prevent the circuit of relay 329from being interrupted prematurely by the operation of busy relay 327during the rotary, movement in case test wiper 340epasses over groundedtest contacts.

The operation following the termination of the rotary movement dependsupon wheth- Assuming first that the called line is busy, busy relay 327is operated when the wipers come to rest on the bank contacts ofthecalled line, and, when the calling subscriber finishes dialing andlistens, he hears the busy tone caused by an application of busy-tonecurrent from the busy tone conductor. 810 through contacts of relay 330and 327 to the lower talking conductor.

With relay 327 operated and relay 329 at normal, the circuit of relay329 is opened a so that relay 329 cannot operate again.

Relay 328 falls back responsive to the de-- energization of relay 329and completes a locking circuit for the bus relay 327 to the lockingconductor 344 y way of the middle upper. armature of relay 327.

earing the busy tone, the calling subscriber is expected to replace hisreceiver andbrin'g about the release of the lineswitch and theconnector. "Assuming now that the line of substation A2 is idle whencalled, the busy relay 327 is not energized when the wipers come to reston the contacts of the called line and the deenergization of relays 329and 328 is followed by the energization of relay 330. The circuit ofrelay 330 is-from ground by way of the grounded conductor 344, throughthe middle-upper armature, normal, of relay 327, ninth-level shaftspring 333 and its lefthand contact,-lower winding of relay 330, upperarmature of relay 328, middle-upperarmature of relay 330, test wiper340, and thence by way of the bank contact on which wiper 340 isstanding, to battery through the cut-off winding of the lineswitch (notshown) associated with the line of substation A2. The bridge-cut-oiirelay of the lineswitch associated with the called line now optracedcircuit, it lock itself to conductor 344 at its inner-upper armature, atthe same time preparing a locking circuit for relay 326 independent ofthe upper armature of relay 329. At its middle-upper armature, relay 330disconnects wiper 340 from the test circuit and connects it directly toground; it prepares a circuit for pick-up relay 331 at its upperarmature; it shifts the operating circuit from the rotary magnet 338 tothe operating magnet 354 of the associatedcode selector CS2; it preparesto place ground on the common interrupter start conductor 622 atarmature 356; at armature 357 it opens a point in the busy-tone circuitso as to prevent the busy tone from being applied to the line upon theoperation of busy relay 327, when it occurs after the code switch isoperated; and at its lower armature it opens a point in the dial-tonecircuit so as to prevent the dial tone from being heard after thering-cut-ofi relay 326 is subsequently operated.

When the next and last digit, the stations digit, is dialled, theresulting impulses are delivered now to the operating magnet 354 of thecode switch CS2, owing to the operated condition of the inner-lowerarmature of relay 330, with the result that the wipers 351 and 352 ofthe code switch CS2 are advanced to a position corresponding to the codeof the called substation. It may be pointed out here that the codeswitch is arranged to signal any one of ten parties on a called line, itbeing assumed that half the ringers are connected between one conductorof the line and ground and the other half connected between the oppositeconductor of the line and ound. In this way, ten parties may besignalled by means of five codes, the selected code being applied to oneconductor or the other depending upon the station called. 'In

wiper 352 on its fifth contact to the lower' winding of ring-cut-oflrelay 326. The completion of the two connections just described is ofcourse dependent on the subsequent operation of pick-up relay 331.

When the wipers of the code switch CS2 come to rest and relay 329fallsback, relay 327 is operated through contacts of relay 329 and throughthe off-normal contacts 3530f the code switch CS2. Upon operating, relay327 places ground on the common interrupterstart conductor 622 atarmature 346 through contacts of relays 330 and 322; at its innerlowerarmature it opens the operating cir cuit; and at its upper armature itconnects the ick-up conductor 713; topick-up relay,

331 y way of the upper contacts. of relay 330. The ringinginterrupter'of Fig. 7 and:

the tone equipment of Fig. 8 -are now operating in a manner to behereinafter described,

and during the operation of the ringing inthe called line by way ofwiper 351, signal-' ing the subscribed at'substation A2..-

When the subscriber at substation A2 responds, a loop is closed acrossthe conductors of his line, whereupon the lower Winding of relay 326 isenergized over the called line, the current flowing to the called lineby way of the fifth contact in its bank, and Wiper 352, contacts ofrelays 326 and 331, and wiper 342. The return circuit to ground issimilar except that it follows the upper conductor of the called lineand wi ers 339 and 351 and is completed by way 0 #5 code conductor. Uponoperating, ring-cut-ofi relay 326 completes its locking circuit at itsinner-up- I per armature from the grounded conductor 344 by way of theinner-upper armature of relay 330.

At its upper and middle-lower armatures, relay 326 opens the ringingcircuit and completes the talking circuit. Back-bridge relay 322 nowoperates over the called line and reverses the incoming line conductorsas regards their connections with the windings of line relay 323, forthe purpose of metering or the like. At its lower armature, relay 322disconnects ground potential from the common interrupter start conductor622, while atits upper armature it makes a second application of groundpotential to the release trunk conductor 309 so as to prevent therelease of the line switch LS1 while the connections to the linerelayare reversed.

The conversation may now take place. When the conversatlon isterminated, the

two subscribers replace their receivers. vOn

the assumption that "the subscriber at substation A2 replaces hisreceiver first, back-bridge relay 322 fallsback and again reverses theconnections of the line relay to their normal condition, at the sametime removing the and the oil-normal contacts multiple ground connectionfrom conductor 309' and again applying a ground potential to theinterrupter start conductor 622.

When the receiver is replaced at the calling substation, line relay 323falls back and short-circuits release rela 324, With the re sult thatrelay 324falls ack after a slight interval. Upon so doing, it permitsthe lineswitch LS1 to release by removing ground potential "fromconductor 309 at its upper armature, and it removes ground at OIN pointfrom conductor 344, but this conductor is now maintained groundedthrough the oilnormal contacts 353 of the code switch CS2, and contactsof relays 329, 328, and 327.

At its lower armature,relay 324 removes ground from the tone-startconductor 621 and closes acircuit for the release magnet 355 of the codeswitch CS2. The circuit of this magnet includes contacts of relays 321,and 324, and armature 345, operated, as well as the associated releasesignal relay 376, common to a shelf of connectors. When the releasemagnet of the code switch CS2 operates, the wipers 351 and 352 arerestored to normal,

353 open, allowing relays 327, 330, and 331 to release. When rela 327releases it disconnects the release condiictor from release magnet 355and connects it to release magnet 336 by way of the off-normal contactsassociated therewith. 9

Upon the operation of magnet 336 the wipers 339342 and 343 are restoredto their normal position in the usual manner, and the various off-normalcontacts of the connector restore to their normal condition. Upon thefalling back of relays 327 and 330 the interrupter? start conductor 622is again ungrounded.

The connection is now released and the apparatus involved therein is inreadiness to be used in establishing subsequent connections.

Reverting call on' the line of substation A1 It will be now assumed thatthe subscriber at substation A1 desires to call another subscriber Whosesubstation is on the same line. In order to do this,the subscriber atsubstation A1 removes his receiver and obtains dial tone from a localconnector in the usual manner, following which he dials the digit 9,followed by thestations digit of the calling station and then thestations digit of the called station. When the digit 9 is dialled, thelocal connector in use is operated to the ninth level and seizes aring-back switch, such as the ring-back switch BB1, Fig. 4, in a mannerto be described more in detail hereinafter, and the ring-back switchresponds to the two stations digits and conditions itself to perform thesignalling operation after the calling subscriber hangs up.

It will be assumed that the local connector LCl of Fig. 3 is the oneseized by the lineswitch LS1 when the receiver is removed at substationA1, in which case the connector is lli) prepared for operation in themanner hereinefore described by the-operation ofrelays 323, 324, and326.

When the first digit is dialled, the wipers 339-342 are raised oppositethe ninth level of bank contacts: The arrangement involving the verticalwiper test 343 is for the purpose of causing the local connector LCl toact as a single digit connector when a reverting call is made. Since thewipers are now raised to the ninth level, wiper 343 encounters the ninthassociated bank contact, which is grounded as may be seen in thedrawings.

This places a ground potential on the rotary test wiper 341 and alsoplaces a ground potential on the regular busy test wiper 340 on accountof the fact that the wiper 343 contacts also with the bank contactimmediately below the contact on which it is standing, the eighth bankcontact in this case. It will be recalled that relays 326, 328, and 329are in operated condition at the end of every vertical movement. In thiscase, since wiper 340 is'grounded by way of the vertical wiper 343 fromground on its ninth contact and by way of its eighth contact, busy relay327 is operated and at its inner-upper armature it connects theresistance 337 in parallel with relay 328 so as to form a path forcirculating current tomake relay 328 slow acting. Relay 328 isordinarily not slow acting so as not to delay the switching operationwhen an idle line is reached.

When relay 329 falls back at the end of the vertical movement and opensthe circuit of relay 328, relay 328 is slow acting and does not fallback immediately owing to the fact that the resistance 337 is in shuntof it at this time. With relay 328 thus operated, and with relay- 329restored and ground potential encountered by the vertical wiper 343, acircuit from ground is closed for relay 325 by way of wiper .343, theinterrupter contacts of rotary magnet 338, and contacts of relays 329and 328. Upon operating when this circuit. is closed, relay 325 closes alocking circuit for itself at its lower armature through the interruptercontacts of the rotary magnet" closes a circuit at its upper armature torelay 328 operated; and at its inner- 1101i lower armature itdisconnects the rotary magnet 338 from in parallel with relay 329 andcloses a circuit for the rotary magnet to ground. The rotary magnetoperates'and it rotates the wipers 339-342 and 343 one step. Near theend of its stroke, magnet 338 opens the circuit of relay 325, whereuponrelay 325 falls back and opens the circuit of magnet 338 at itsinnerlower armature. Obviously, relay 325 opens a point in its lockingcircuit at its lower armature and opens the circuit of the nowslow-acting relay 328 at its upper armature. v has been rotated awayfrom engagement with its vertical set of contacts with the result thatthe further operation depends u on whether the "trunk lme leadin toatherst ring-back switch is busy or id e. If it is busy, wi er 341encounters a grounded contact wit the result that relay 325 operatesagain thereover and busy relay 327 remains operated over the encounteredgrounded contact and maintains relay 328 shunted by resistance 337 so asto maintain it slow acting. In this case the rotary magnet 338 isoperated again and the wipers advance another step. This alternateoperation of relay 325 and magnet 338 continues until an idle trunk lineis reached, whereupon relay 325 fails to operate again and relay327falls back. When relay 327 falls back, the shunt 337 is removed fromaround the, winding of relay 328 and this relay immediately falls backand connects up the test wiper 340.

With relays 327 and 328 both deenergized, a test circuit is closed fromground on conductor 344 to battery on the release trunk conductor 365 byway of wiper 340 and the bank contact on which it is standing. This isunder the assumption that the ring-back switch RBl is idle when testedand is, therefore, seized. The test circuit at this time includes thetest winding of switch-through relay 321 instead of the test winding ofswitching relay 330 on account of the fact that the ninth-level shaftspring 333 is now shifted to its alternate position. The completecircuit for the upper winding of relay 321-is as follows: from ground byway of the grounded conductor 344 (grounded as hereinbefore pointed outat the middle upper armature of relay 324), middle-upper armature,normahof relay 327 ,spring 333 and its right-hand contact, upper windingof relay 321, resting contact and upper armature of relay 328,middle-upper armature of relay 330, test wiper 340, the bank contact onwhich 'it is standing, conductor 365, lower armature,

normal, of relay 402, Fig. 4, jumper 429, upper armature, normal, ofrelay 425, and resistance 430 to battery.

Upon operating, relay 321 closes a locking circuit for its lower windingat its inner-upper armature to the groiinded release conductor 309, andat the same time it joins release conductor 309to the test wiper 340 byway of contacts of relays 328 and 330. At its inner-lower armature,relay 321 opens a "point in the operating circuit; it opens a furtherpoint in the release circuit at its middle-lower armature and closes analternative tone-start circuit; and at its upper and lower armatures itdisconnects the incoming conductors 308 and 310 from the talkin circuit(including the front and backbrldge relays 323 and 322) and extends themdirectly to the wipers 339 and 342. When this is done, line relay 424 ofthering-back ductors 364 and 366 through contacts of relay 421, operatesover the calling line and through the wipers 339 and 342 of the localconnector LCl and closes a circuit for release relay 425 through theoperating magnet 433. Release relay 425 energizes and prepares theswitch for operation at its lower armatures and closes a holding circuitfor the connector and line-switch at its upper armature by placing aholding ground potential on conductor 365. Since conductor 365 is nowjoined, as above pointed out, to release trunk conductor 309 of thelocal connector LCl, the line switch LS1 remains operated and relay 321of the connector LCl remains energized through its lower winding.

When line relay 323 is cut off by the operation of the upper and lowerarmatures of relay 321, it falls back and short circuits relay 323, withthe result that relay 324 falls back after an interval, but theconnector LCl does not release owing to the fact that relay 321 isoperated.

. The calling subscriber now dials the digit corresponding to his ownstation suffix, whereupon the line relay 424 of the ring-back switch BB1falls back a corresponding number of times. Each time it does so, itcloses at its make-before-break contacts a circuit for the operatingmagnet 433 of the digit register DB1 as follows: from ground by way ofthe resting contact and middle-lower armature of relay r428, contactscontrolled by line relay 424, inner-lower armature of release relay 425,inner-lower armature, normal, of relay 428, and the inner-lowerarmature, normal, of relay 427 to battery by way of the operating magnet433. By the operation of operating magnet 433, wipers 435 and 436 arepositioned on the contact set corresponding to the suflix assigned tothe calling substation. It will be noted that relay 425 is shortcircuited on each impulse delivered to the operating magnet but this 4relay remains operated in the manner pointed out in connection withrelease relay 324 of the local connector LCl. Relay 426 operates inmultiple with the operating magnet upon the first closure of the circuitto the latter and it remains operated throughout the series ofdeenergiza-tions of relay 424 for the reason pointed out in connection"with relay 329, Fig. 3.

'When relay 426 falls back at the end of the stations digit assigned tothe calling station,

the lower winding of transfer relay 427 is energized through theoff-normal contacts 432 of the digit register DB1 and through thenormally closed contacts controlled by the armature of relay 426.

The calling subscriber now dials the digit assigned to the desiredstation on the calling line, whereupon line relay 424 is againdeenergized a corresponding number of times. Each deenergizationoccurring at this time results in the closure of a circuit for theoperating magnet 438 of the digit register DB2 owing to the operatedcondition of the rela 427, which transfers the operating circuit frommagnet 433 to magnet 438 at its inner lower armature. It will be notedthat, when relay 426 operates at the beginnin of the second series ofimpulses, the initia circuit of relay 427 is opened, but an alternatecircuit is closed for the relay through its upper winding by way of itsupper contacts.

When relay 426 falls back at the end of the digit,it completes a circuitfor the lower winding of relay 428 through ofl'-normal contacts 437, andagain completes the initial circuit forthe lower winding of relay 427.Belay 428 disconnects the operating circuit from magnet 438 at itsmiddle-lower armature and transfers it instead to relay 421 by way ofthe normally closed contacts controlled by the inner-lower armature ofrelay 422. This extension of the operating circuit, it will be noted, ismade to the upper terminals of relay 421, whose lower terminal isconnected to battery through the operating magnet 433. Belay 421isaccordingly connected in series with the operating magnet 433 andrelay 425, but is short-circuited at the armature of relay 425.

It will be noted that the ground potential is removed at the lowerarmature of relay 428 from the spring combination controlled by thearmature of line relay 424. This is done so as to prevent relay 425 frombeing short circuited upon the nextadeenergization line relay 424.

Having dialled the required stations digits, the calling subscriber atsubstation A1 replaceshisreceiverto allowthe ring-back process to takeplace. When this is done, relay 424 falls back and removes the shortcircuit from around relay 421. Belay 425 is now held operated in acircuit including its own inner lower armature, inner-lower armature,operated, of relay 428, normally closed contacts controlled by theinner-lower armature of relay 422, relay 421, and operating magnet 433.Belay 421 now operates in this holding circuit in series with relay 425and at its lower armature places ground on the "interrupter startconductor 622; it connects the pick-up conductor 713 to pick-up relay423 at its inner-upper armature,and at its two uppermost armatures itdisconnects the incoming conductors 364 and 366 from the windings ofline relay 424 and connects them instead to the ringing circuit.

When the ringing interrupter of Fig. 7, which is started responsive tothe grounding of interrupter start'conductor 622 by relay 421, 1

arrives in its pick-up osition and grounds the pick-up conductor 7 13,pick-up relay 423 operates through contacts of relay 421 and locksitselfto ground through the inner-upper armature of relay 425, at the sametime openlower winding of ring-cut-ofi' relay 422 to their contactbanks.

- the lower right-hand ing coil 431 by way coil 431 to one sent backover ing its initial circuit. At the middle-upper armature of relay 423,a ground potential is7 appliedto the lower left-hand repeating-coilterminal through contacts of relay 421, and at the upper contacts ofrelay 423 the connection is completed from conductor 364 through thewiper 440. At its three lower. armatures, relay 423 connects up thefirst and third and fifth code conductors to the bank of the digitregisters DB1 and DB2. These conductors are normally open so as toprevent sparking occasioned by the passage of the wipers of the digitregister DB1 and DB2 from contact to contact.

The ringing current now sent back to the line of substation A1 dependsupon'the relative setting of the re isters DB1 and DB2. In case theringers of t e calling and called stations are connected to oppositesides of the line, it is necessary to send out the code of the callingstation on one side of the line in addition to sending out the code ofthe called station on the other side of the line so that the calling manwill know, by the cessation of his code, when the called man hasresponded, but if both ringers are connected between the same side ofthe line and ground, it is necessary to send out only the code of thecalled substation, as this code is then heard at both substations.Assume, for example, that both ringers are connected between the upperline conductor and ground. In this case, the last two digits will befrom one to five in both cases and the wipers of the digit registers DB1and DB2 will be set on the first half of In this case, the position ofwiper 440 directly determines the code sent to'the line through theupper talking conductor, as it directly contacts with one of the livecode conductors, while the wiper 441 extends terminal of the repeatfivecontacts in its banks to wiper 436. This terminal is not furtherextended by wiper 436, however, onaccount of the fact that the firstfivecontacts in its bank are left dead.

If it is assumed that the ringer of the calling station is connectedbetween the lower conductor of the line and ground, the stations digitassigned thereto is any one from six to 0, with the result that thedialling of this digit-results in the digit register DB1 being set on abank conta ct set ofthe second half. In this case, the wiper 436 extendsthe lower right-hand terminal of the repeating of the code conductors. sa result, the code of the calling subscriber is the lower talkigconductor, owing to the repeating action of t e repeating coil 431, atthe same time that the code of the called party is sent back overtheupper conductor. It is the necessity for the simultaneous signallingover both conductors that gives rise to the repeating coil 431, which isstation on the calling line.

of any one of the first one of the code conductors directly used inorder that a battery potential may be present at all times on the lowertalking conductor so as to form a circuit for the lower winding of thering-cut-ofl? relay 422 at any time that the receiver may be removed atany It will be noted that, in case the digit used to set the digitregisters DB2*is any one from 6 to O. the wipers 440 and 441 are set on.the second section of the banks and it is the lower conductor uponwhich the ringing current is impressed by wiper. 441 through the mediumof the repeating coil 431, while whether or not ringing current isimpressed upon the uppersconductor by Wiper 440 depends upon thespecific setting of wiper 435. If the digit register DB1 is set on thesecond section of its bank, the wiper 435 merely encounters the groundpotential for completing the circuit of the ring-cut-ofi relay and noringing current passes out overthe upper talking conductor, because bothringers are connected between the lower conductor of theline and groundand both the calling and the called party hear called substation. On theother hand, if the calling substation is one whose ringer is connectedbetween the upper line conductor and digit register DB1 is set in ac- 1to 5 and the ground, the cordance with a digit from upper conductor isextended to .a code conductor by wiper 435 in the first half of itscontact bank. 1.,

At any rate, the calling party hears his own code transmitted back tothe calling line over the conductor to which his ringer is connected,and at the same time that the other code is transmitted back over theother side of the line, or else he hears only the code of the calledsubstation in case both ringers are connected between the same side ofthe line and ground.

Assuming first that the called party does not respond, the callingsubscriber removes his receiver and to clear out the ringing equipmentand cause the connection'to be released in a manner to be hereinafterdescribed.

Assuming now that the subscriber at the called substation responds, acircuit is completed for the lower winding of ring-cut-ot'f relay 422 toground by way of wiper 440 and or through wiper'435 and one of the codeconductors or through wiper 435 and ground directly. The return path forthe operating circuit of relay 422 is to battery by way of the uppering, relay 422 closes alocking circuit for its upper winding at itsinner-upper armafor relay 425 at-its" lower armature; and at againreplaces it in order the code assigned to the 3 Winding of repeatingcoil 431. Upon operaty it "prepares again the shunt 4 its inner-lowerarmature it, connects relay f 426 (in parallel with operating magnet 4383 through the inner-lower armature, operated net 433 in series.This-leaves a holding cir-" cuit established for relay 425 through itsown inner-lower armature, the inner-lower armature, operated, of relay427 and the operating magnet 438. 4

Relay 421 falls back at this tinie and removes ground from theinterrupter-start conductor 622 at its lower armature, at the same timeshort circuiting relay 425 through its lower armature and restingcontact, corresponding armature of relay 422, 'middlelower armature ofrelay 428, and the contacts of the armature of relay 424. 1 The placingof this short circuit around relay 425 closes the usual operatingcircuit for relay 426 and the magnet 438. This operating circuit isusually opened, however, before the relay and magnet have had time tooperate and in a manner to be now described: At its two uppermostarmatures relay 421 transfers conductors 364 and 366 back to thewindings of line relay 424, whereupon line relay 424 again operates andestablishes the regular circuit for relay 425 in series with operatingmagnet 433, removing the short circuit from around relay 425. v

The two subscribers may now converse with each other in the usualmanner, the transmit,- ters at the two substations being supplied withtalking current through the windings of relay 424.

It may be pointed out that, in case the ring-back switch RBI is used inconnection with a connector or other first switch in the train whichdoes not employ a dial tone, the jumper 429 is removed from between theassociated terminals, with the result that, when ring-cut-ofi relay 422operates, it removes ground from the holding conductor 365 and bringsabout the immediate release of the connection. The line switch LS1 ofthe calling line releases in that case and takes a new trunk line andthe transmitter current is supplied from the line relay of the firstswitch of the train. In the present case, however, since dial tone issupplied to the calling line by the connector LCl the jumper is left inplace, as the dial tone would interfere with the conversation. 7

When the two subscribers replace their receivers at the end of theconversation, line relay 424 falls back and again short circuits releaserelay 425 through contacts of relays 428, 422, and 421 as above pointedout, incidentally operating relay 426 and the magnet 438. After aninterval, relay 425 falls back and removes the holding ground fromconductor 365 at its upper armature, opening the circuit of relay 426and magnet 438 at its inner-lower armature.- At its lowerar-mature,relay425 removes ground from'the tonestart conductor and closes acircuit through the associated shelf-supervisory relay for releasemagnet 434 of the digit register'DRl magnet 439 operates and causes thedigit register DR2 to restore. Off-normal contacts 437 open anddeenergize relay 428, which falls back and opens the circuit of releasemagnet 439 at its lower armature. The common release-signal relay is, ofcourse, energized in series with either of the release magnets and fallsback when the circuit of the: last release magnet is opened.

In the local connector L01, relay 321 falls back when the groundpotential is removed from release-trunk conductor 365 of the ringbackswitch RBl and closes the release magnet circuit at its lower armaturethrough contacts of relays 324 and 327. When this occurs, release magnet336 operates and restores the connector to normal position in the usualmanner.

Operation of the trunk-Maytag relays I times happens thata ring-backswitch such as the ring-back switch RBI becomes defective and does notoperate properly, or that one of the conductors leading thereto becomesopen. Since this ring back switch is first choice to the severalconnectors, repeated attempts during light traflic to make a revertingcall may all fail if the same ring-back switch is taken for use in eachcase. On the other hand, if there is an alteration so that the firstcall takes the first ring-back switch and a second call must take thesecond ringback switch before the first is again rendered available forservice, the second attempt to make a reverting call results in thesecond choice switch being taken for use over the conductors 367369.

In order to accomplish this result of alternating between the first tworing-back switches the relays 402404 are provided, and they operate asfollows: When the ringback switch BB1 is taken for use and the releasetrunk conductor 365 is grounded, a cir- 404. This locking circuit doesnot become eifective and no current flows through it as long as theground potential is maintained on conductor 365. When, however, theground potential is removed from conductor 365 401 at the same timeopening t e circuit of relay 403. After a slight interval, relay 403falls back and applies a guarding potential to conductor 365 at itslower armature through the lower armature of relay 402. The delay in theapplication of this guarding potential to conductor 365 is of sufficient1nterval to permit the connector involved in the connection to restore.With relay 402 operated and relay 403 restored, relay 404 is connectedto the release trunk conductor 368 of the ring-back switch BB2 throughcontacts of relays 402 and 403. 7

When the next reverting call is made, the trunk line comprisingconductors 367-369 leading to the ring-back switch BB2 is seized onaccount of the fact that the trunk line leading to the switch BB1 ismade artificially busy, as above explained. When this trunk line isseized, relay 404 operates and opens the circuit of relay 402 whereuponrelay 402 falls back and removes the guarding potential from theconductor 365 to permit the next call to come in to the ring-back switchBB1. It will be understood, of course, that there may be other ring-backswitches in addition to the two shown,, in which case one of theremaining switches is taken any time a reverting call is made when thefirst two are in use.

Hall from the 0. A. X. to the manual ewahange It will now be assumedthat the subscriber at substation A1, Fig. 3, desires to converse with asubscriber whose line terminates in'a manual exchange, a part of, theequipment of which is shown in Fig. 1. It will be assumed further thatthe line switch LS1, upon operating when the receiver is removed at thecalling substation, seizes the local connector LC1 in which case theconnector LCI is prepared for operation in the usual manner. When thefirst digit 0, of the number 01 assigned as the call number of themanual ofiice, is dialled, the wipers 339-342 are raised opposite the.tenthlevel of bank contacts, and wiper 343 contacts with the tenthassociated bank contact. Wiper 343 also bridges from the ninth contacttothe tenth contact, causing wipers 340 and 341 to be both grounded asin the case of a reverting call. Relays 328 and 329 are energized asbefore, and,'as soon as relay 329 falls back at the end of the verticalmovement, it completes the circuit for stepping relay 325 from 'the'grounded wiper 341 through contacts of relay 328. The first rotary stepis accordingly taken to advance the wipers 339-342 onto the first set ofcontacts in the tenth level and to cause the wiper 343 to disengage thevertical contact strip.

The rotary movement continues beyond the first bank contact set orstops, depending upon whether the first trunk line is busy or idle. Itwill be assumed that the first trunk line is idle and that the movementaccordingly stopxs. In this case, the busy relay 327 falls bac as doesrelay 328, and relay 330 is energized throu h its lower winding aspointed out hereinbe ore in-connection with a-call between substation A1and substation A2. The energizing circuit at this time includes the testwiper 340, as before, and is completed now to battery over the firstcontact in the tenth level, test conductor 371, contacts of relay 262,release trunk conductor 209 of the incoming connector I0, upperarmature, normal, of relay 224, the associated ofi-normal spring and itslower contact, and the lower winding of rela 221 to battery. Uponenergizing over t is circuit, relay 330 disconnects the operatingconductor from the rotary magnet 338 at its inner-lower armature andextends it to theoperating magnet of the code switch CS2 with the resultthat, when the calling subscriber dials the next digit 1,

the code switch CS2 is operated to enable ringing current to betransmitted over the trunk ine TL1 associated with the incomin connectorIC.

11 the mcomlng connector IC, relay 221 operates as a cut-off relay anddisconnects conductors 208 and 210 from the'portion of the talkingcircuit including the front and back-bridge relays 222 and 223, so as toclear the line for ringing current. With ground otential applied toconductor 209, a current fiows through the upper winding of theelectro-polarized relay 204, but the relay is not operated by eitherwinding alone'due to the design of the windings of the relay.

When the ringing current is applied to the wipers 339 and 342 of theconnector it passes over conductors 370 and 372 to the right-handwindings of the repeating coil associated with the alarm circuit ALCKT.The ringing current is repeated into the left hand windings of therepeating coil, and passes over the conductors of the trunk line TL1 tothe manual oflice and is again repeated through the repeating coil thereand operates the ring-up relay 107 through contacts of the cut-off relay106. Upon operating, the ring-up relay locks itself operatedmechanically under the control of the cut-off relay as is commonpractice in connection with the ring-up and cut-ofi air. The ring-uprelay closes a circuit for t e answering lam 108.

When the operator notes the light condition of the answering lamp sheinserts the plug of a cord circuit (not shown) into the line ja'ckLJ,whereupon the sleeve relay 106 operates "over the sleeve of the jackfrom a battery potential applied to the sleeve of the plug of the cordand mechanically unlocks the ring-up relay 107 and permits it torestore. At its upper armature, relay 106 reand 372 are reversed betweenthe bank mulassists the current flow in the upper winding on account ofthe fact that conductors 370 'tiple and the conductors 208 and 210 asshown. Upon operating, relay 204 shifts the connection to relay 205 sothat the high resistance upper winding is included in series with thelow resistance lower winding. ThlS I decreases the current flow over thetrunk line TL to such an extent that relay 104 is unable to operate andcomplete the circuit of the supervisory lamp 109, which is prepared byrelay 105, energized through the lower armature of relay 106.

The operator now converses with the calling subscriber and extends theconnection to the desired line in the usual manner.

When the ensuing conversation is terminated, the subscriber atsubstation A1 replaces his receiver whereupon the connector L01 and theline switch LS1 release in the usual manner and the ground potential isremoved from conductor 371. When this occurs, relays 204 and 221 fallback. Relay 204 increases the current flow over the trunk line TL byshifting the connections of relay 205 back to normal, whereupon relay104, Fig. 1, operates and closes a circuit for supervisory lamp 109 soas to cause the lamp to become lighted as a disconnect signal.

When the operator perceives the disconnect signal, she pulls down theconnection, whereupon relays 104106 fall back and relay 205, Fig. 2,falls back as a result of the opening of the circuit over the trunkline.

In the interval between'the replacing of the receiver by the subscriberat substation A1 and the pulling down of the connection by the operator,a circuit is closed for line relay 223 of the incoming connector 10 withthe result that the connector is prepared for operation in the usualmanner, but this op-, eration is merely incidental and its chieffunction is to guard the trunk line from seiz ure in the O. A. X. aslong as the operator has the connection up in the manual exchange.

e connector is restored to .its normal condition when the relay 205falls back.

It will now be assumed that the operator in the manual ofiice receives acall to be comleted to the line of substation A2 in the O. A. El.Assuming that the trunk line TL1 is idle, the operator may insert thecalling plug of her cord circuit in use into the line ack LJ, resultingin the energization of relays 106 and 105 and the energization of relay104 over the trunk line TL1. Lamp 109 becomes .li hted as a supervisorylamp.

.tion in a manner explained in connection with the local connector L01and in addition short circuits the resistance 244 at its inner-lowerarmature. It may be pointed out at this time that the incoming connectorIO and the code switch CS1 taken together are almost identical with thelocal connector LCl and the code,

switch CS2, and that they difier only in slight details to be fullyexplained. For this reason it will be considered unnecessary to repeatthe description of the operation of the incoming connector 10 in all itsdetails.

In the manual oifice, the o erator inserts the plu of the dial cord Dinto the dial jack D after she has taken the trunk line for use, and sheproceeds to operate the calling device CD in accordance with the threedigits in the number of the line of substation A2.

When the calling device CD is first turned off-normal, a circuit iscompleted through the ofl'-normal contacts thereof and over the tip ofthe plug and jack for relay 101. Relay 101 disconnects the simplex legof the trunk line TL1 from ground through relay 104 and connects itinstead to ground through the ring contacts of the ack and plug and theimpulse contacts of the calling device CD. As a result, each time theimpulse contacts are opened on the return movement of the calling deviceCD the circuit of the repeating relay 205, Fig. 2, is opened. Relay 205falls back a number of times corresponding to the digit dialled andrepeats the interruptions produced in its circuit into the circuit ofline relay 223. As a result of this vertical magnet 235 is operated inthe manner described in connection with vertical magnet 335, Fig. 3, andthe wipers 239242 are raised opposite the desired level of bankcontacts.

When the next digit is dialled, rotary magnet 238 is operated to advancethe wipers 239-242 into engagement with bank contacts in which the lineof substation A2 terminates,

and, if the line is idle, relay 230 operates to seize the line and toextend the operating cirthe result that th called line'is signalled.

cuit to the operating magnet 254 of the code switch CS1.

When the stations digit is dialled, the code switch CS1 operates in themanner'described in connection ,with the code switch CS2 with When thecalle subscriber answers, ringcut-ofi relay 226 operates and removes theringin current and completes the talking circuit. ack-bridge relay 222operates at this time and reverses the incoming conductors 208 and 210in regard to their connection with the windings of line relay 223,whereupon'the.

electro-polarized relay 204 operates and gives 5 answering supervisionto the calling operator by causing relay 104 to fall back and open thecircuit of supervisory lamp 109. L Upon perceiving the disconnect--signal I when relay 104 operates again under control ,differs from theconnector LC1 will now be explained. The 'ofl-normal spring locatedabove relay 222 is for the purpose of guarding the connector 10 fromseizure'by a connector such as the connector LCl while the connector ICis releasing. At this. time relay 224 is at normal, but the oif-normalspring mentioned abgve is in engagement with its grounded upper contact,placing a guarding ground potential on conductor 209 by way of the upperarmature of relay 224. When the normal position is reached, the saidolfnormal spring moves into the position' shown 0 inthe drawing,rendering the connector idle.

Since the connector cannot release until the code switch CS1 releasesand permits relay 227 to fall back, the connector is held guarded incase either it or the switch CS1 is unable to release.

The resistance 244 is provided to prevent 23 sufficient current flowthrough magnet to cause eventual damage in case the conductor 208becomes grounded just sufiiciently to cause the'armature of line relay223 to move over against its contacts, but not enough to move it all theway. In this case relay 224 remains short circuited and'resistance 244is not shunted as it is when relay 224 operates.

With reference to the trunk busying relays 262-264, these relays operatein'the same from the manual oflice alon with the local connector LC1.The multip e is left intact between the incoming connector and the localconnector LCI on the ninth and tenth levels so that the operator in themanual ofiice can test the ring-back'switches and themanualto-automatictrunk lines.

Giving trouble alarms- In case an abnormal condition arises within theP. A. X., such as the failure of one or the other charges to start,thefailure of the ringing machine, or the sticking of a connector in anoil-normal position or'the blowing of afuse, it is necessar that analarm be given or that the conditlon be indicated so that the defect maybe remedied. In case the trouble consists in a fuse of a local connectorbeing blown or "the connector stuck in an oil-normal position, there isno emergency existing and there is'no need of sounding an alarm to getthe same prompt action :as would be required in case of the failure ofthe ringing current, for example.

This difi'erence in the importance of the various trouble conditions isrecognized in the present disclosure in the division of alarms intotwo-classes, regular alarms and emergencyalarms.

The relays lar-alarm relays, and the. relays 556-560 manner as relays402-404, Fig. 4, in order to make the trunk line extending to theincoming connector IC artificially busy, after 0 it has been used,until'the trunkline TL2,

which is the second trunk of the group, has been used.

It will be noted IC has access to the ring-back switches of as Fig. 4and also to the trunk' lines incoming that the incoming connector arethe emergency-alarm relays.

More in particular, relay 554 of the first group is the one whicheventually operates in case there is aregular alarm existing-and relay559 is the relay of the second group which operates tosound an emergencyalarm. The way in which these relays'are operated will be explainedmore-in detaiP-hereinafter. At this time it will be merely assumed thatrelay 554 operates to indicate a sci-called regular-alarm condition suchas the failure of a connector to release, in'which case it closes acircuit at its lower armature for relay 562. Relay 562, upon operating,closes a circuit at its upper armature for the local buzzer 531 whichsignals an attendant in case one is present. making a repair, forexample. At its lower armature, relay 562 closes a -circuit for relays563 and 564 in series with the associated resistance. Relay 563 isnormally short circuited by the contacts of relay 564 and relay 564operates 'first and removes the short circuit from around relay 563.Relay 563 then operatesand short circuits relay 564, causing relay 564to'fall back and again short circuit relay 563. This action continueswith the relays 563 and 564 alternatin Each time relay 564 operatesitopens t e circuit that is normally closed through contacts of relay561 from battery through resistance 565 and over conductor 547 to thenormally energized relay 201 i in the] alarm circuit AL.CKT. When relay201 ,falls back, it closes at its lower armature a circuit for thebuzzer 202 in 551-555, Fig. 5, are the regu-

